This invention relates to an integrated circuit device for use in an electrical circuit in which data is supplied to another device which may operate at a different voltage.
Conventional integrated circuit devices operate with different rail and input/output voltages, and special steps need to be taken to connect them to one another when different rail voltages are used for the individual devices. For example, in a mobile telephone handset, the major telephony functions are controlled by a micro-controller, which is driven by a power supply at a predetermined rail voltage e.g. 1.8 v. The power supply is driven by a rechargeable battery in the handset. Conventionally, the level of charge in the battery is monitored by a current sensor that comprises an integrated circuit which feeds data to the controlling microprocessor. The current sensing integrated circuit is typically driven by the voltage of the battery, which is different from the supply rails for the controlling microprocessor. Nevertheless, the current sensor integrated circuit needs to supply its data to the controlling microprocessor at a voltage compatible with the input/output voltage used by the microprocessor.
One approach used hitherto has been to provide a connection pin on the current sensor integrated circuit to receive a rail voltage supplied by the controlling microprocessor. The integrated circuit uses the voltage applied to the pin so as to configure its data output supplied to the controlling microprocessor, to be at a voltage corresponding to the input/output voltage for the microprocessor. Additionally, the current sensor integrated circuit includes an enable pin which receives an enabling signal from the microprocessor to control its operation, i.e. to enable it to produce data corresponding to the condition of the battery. Thus, the current sensor integrated circuit can use its own supply rails, at a different voltage from the controlling microprocessor, yet produce a data output compatible with the microprocessor.
A problem with this approach is that the number of pins needed increases the overall size of the integrated circuit package and undesirably uses up space in the handset. This problem occurs not only in relation to the current sensor integrated circuit but also other situations in which communication occurs between integrated circuits that operate with different rail voltages.
The present invention seeks a solution to this problem. According to the invention there is provided an integrated circuit device including: a circuit configuration to be driven from supply rails at a given operational voltage, pins for connection to supply rails for the device to receive said operational voltage, a data pin to supply data to another device that may operate at a running voltage different from said operational voltage for the device, an enable pin to receive an enabling signal from the other device at the running voltage thereof, the circuit configuration being enabled to supply data for the other device to the data input pin in response to the enabling signal applied to the enable pin, and control circuitry responsive to the enabling signal to control the voltage of the data fed by the circuit configuration to the data pin to be compatible with the running voltage of the other device.
The control circuitry may comprise an impedance coupled between the enable pin and the data pin, and a switch operable to connect the data pin to one of the rails so as to move the voltage of the data pin in accordance with said data between a voltage corresponding to the voltage at the enable pin and the voltage of said one of the rails.
Alternatively, the control circuitry may comprise a gate configured to supply the data to the data pin, the gate being controlled in accordance with the voltage at the enable pin.
Thus, in accordance with the invention, there is no need to provide a pin to receive the rail voltage corresponding to the running voltage from the other device, since the integrated circuit device includes control circuitry responsive to the enabling signal so as to control the voltage of the data fed by the circuit configuration, to be compatible with the running voltage of the other device.
The invention has particular although not exclusive application to battery driven telecommunications apparatus such as a mobile telephone handset in which the integrated circuit device comprises a battery sensor for providing data relating to the level of charge of the battery, and the other device comprises a controlling micro-controller for controlling telecommunications functions.